1. Field of the Invention
The disclosed concept relates to a switch arrangement for an electrical switchgear.
2. Background Information
As is well known, a switchgear is an integrated assembly of switches, circuit breakers, buses (i.e., power supply rails), fuses and other components used to isolate electrical equipment at an electrical installation, for example, an electrical power substation. A switchgear is used to both de-energize equipment to allow work to be done and to clear faults downstream of the switchgear. The switchgear is often housed in a metal housing assembly at the installation. A circuit breaker assembly includes a base and one or more elongated switching elements, such as, but not limited to, vacuum interrupters. The switching element includes an internal set of separable contacts. That is, the switching element may be open or closed as is known. Further, the switching element includes two external contacts, one at the proximal end and one at the distal end. The circuit breaker assembly is structured to move between various positions relative to the housing assembly including a first withdrawn position and a second fully inserted position. The circuit breaker assembly may also be placed in various intermediate positions, as discussed below. The switching elements extend from the circuit breaker assembly base in a cantilever manner with the longitudinal axis extending generally horizontally. Accordingly, as used herein, the end of the switching element adjacent, or directly coupled to, the circuit breaker assembly base is the proximal end and the end of the switching element spaced from the circuit breaker assembly base is the distal end. This convention will be used with other elements of the switchgear as described below.
In one embodiment of a switchgear, the housing assembly includes a conductor assembly including a number of conductive buses, a contact insulator, and a number of contacts. The contact insulator is, in an exemplary embodiment, an elongated hollow, non-conductive body or segmented body assembly. The longitudinal axis of each contact insulator is generally aligned with longitudinal axis of a movable switching element. Thus, as the circuit breaker assembly moves between the positions noted above, the switching element is moving longitudinally in and out of, and through, the contact insulator. Accordingly, the contact insulator includes a proximal end that is closer to the circuit breaker assembly base and a distal end that is spaced from the circuit breaker assembly base. Further, the contact insulator includes a medial portion.
Within the contact insulator hollow body there are three contact assemblies. The contact insulator contact assemblies are spaced apart substantially the same distance as the switching element contacts. The contact insulator contact assemblies are disposed as follows: one contact assembly at the proximal end, one contact assembly in the medial portion, and one contact assembly at the distal end. The various contact assemblies are coupled to, and in electrical communication with, the conductive buses. The conductive buses are further coupled to, and in electrical communication with, a line, a load, or a ground. For example, the distal contact assembly is typically coupled via a conductive bus to, and is in electrical communication with, a line. The medial contact assembly is typically coupled via a conductive bus to, and is in electrical communication with, a load. The proximal contact assembly may be coupled via a conductive bus to, and be in electrical communication with, a secondary line or a ground. As used herein as an example, the proximal contact is coupled via a conductive bus to a ground.
As the circuit breaker assembly moves between the first and second positions, the switching element external contacts engage, and are in electrical communication with, different contact assemblies. For example, when the circuit breaker assembly is in the first, fully withdrawn position, the switching element is spaced from the contact insulator and the switching element external contacts do not contact any of the contact insulator contact assemblies. As the circuit breaker assembly moves toward the second position, the switching element enters the contact insulator and the switching element distal contact engages, i.e. becomes coupled to and is in electrical communication with, the contact insulator proximal contact assembly. In this configuration, the switching element is grounded. As the circuit breaker assembly continues to move toward the second position, the switching element distal contact disengages from the contact insulator proximal contact assembly and moves toward the contact insulator medial contact assembly. The switching element distal contact then engages, i.e. becomes coupled to and in electrical communication with, the contact insulator medial contact assembly. Simultaneously, the switching element proximal contact engages, i.e. becomes coupled to and in electrical communication with, the contact insulator proximal contact assembly. In this configuration, and when the switching element internal contacts are closed, the load is grounded. When the circuit breaker assembly continues to move toward the second position, the switching element contacts disengage from the identified contact assemblies. As the circuit breaker assembly moves into the second position, the switching element distal contact engages, i.e. becomes coupled to and in electrical communication with, the contact insulator distal contact assembly. Simultaneously, the switching element proximal contact engages, i.e. becomes coupled to and in electrical communication with, the contact insulator medial contact assembly. In this configuration, and when the switching element internal contacts are closed, the load is coupled to, and in electrical communication with, the line.
Thus, a contact assembly may be in one of two configurations: a first configuration, wherein the contact assembly is not coupled to and in electrical communication with a switching element external contact, and a second configuration, wherein the contact assembly is coupled to and in electrical communication with a switching element external contact.
The switching elements and the contact insulators typically have a generally circular cross-section. Thus, the switching element contacts and the contact insulator contact assemblies are typically circular as well. The contact insulator contact assemblies are slightly larger than the switching element contacts so as to allow the switching element contacts to move through the contact insulator contact assemblies. The contact insulator contact assemblies cannot, however, be too much larger than the switching element contacts as the contacts must actually contact each other when coupled. This is a disadvantage when the switching element is not substantially aligned with the contact insulator, i.e. when the longitudinal axis of the switching element is not substantially aligned with the longitudinal axis of the contact insulator. When a misalignment occurs, the switching element contacts may not pass through, or into, the contact insulator contact assemblies. Rather, the switching element contacts may engage, catch, or bind, upon the axial face of the contact insulator contacts.
There is, therefore, a need for a contact assembly structured to allow a switching element to pass through a contact insulator contact even when the longitudinal axis of the switching element is not substantially aligned with the longitudinal axis of the contact insulator.